CBSE Class 12 Biology Microbes in Human Welfare Assignment Set C

Very Short Answer Questions

Question. How do mycorrhizal fungi help the plants harbouring them? 
Answer: The mycorrhizal fungi absorb phosphorus from the soil and transfer them to the host cells. They also impart resistance to host plants against root pathogens. They also help plants to tolerate salinity and drought.

Question. Name the source of cyclosporin-A. How does this bioactive molecule function in our body?
Answer: Trichoderma polysporum. It acts as an immuno-suppresant and is used in organ transplant patient.

Question. Give an example of a rod-shaped virus. 
Answer: Tobacco mosaic virus.

Question. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
Answer: ‘Dosa’ and ‘idli’ (from rice), bread (from wheat) and ‘dhokla’ (from Bengal gram) are the traditional Indian foods which involve use of microbes.

Question. Why is distillation required for producing certain alcoholic drinks?
Answer: Distillation increases the alcohol content in alcoholic drinks.

Question. What would have happened if antibiotics were not discovered?
Answer: If antibiotics were not discovered, bacterial diseases would not have been controllable.

Question. Find out the name of the microbes from which cyclosporin A (an immuno-suppressive drug) and statins (blood cholesterol lowering agents) are obtained.
Answer: (a) Cyclosporin A is obtained from Trichoderma polysporum.
(b) Statins are obtained from the yeast Monascus purpureus.

Question. What is the chemical nature of biogas? Name an organism which is known to be employed in biogas. 
Answer: The biogas contains methane, CO₂ and H₂. Methanobacterium, a type of methanogen is employed for biogas production.

Question. Mention the role of cyanobacteria as a biofertiliser. 
Answer: It is a biological organism that fixes atmospheric nitrogen.

Question. Cow dung and water is mixed and this slurry is fed into the biogas plant for digestion by microbes. The person performing the process shares that there is no need to provide inoculum for it, why? What is the role of microbes at the source? Under which condition will they be most active and effective? 
Answer: There is no need to provide inoculum for it because the bacteria, methanogens are present in cow dung. The role of these microbes is breakdown of cellulose. These are most active in an anaerobic condition.

Short Answer Questions

Question. Name any two species of fungus, which are used in the production of the antibiotics.
Answer: Two species of fungus, used in the production of the antibiotics:
(i) Penicillium notatum (for penicillin production).
(ii) Aspergillus fumigatus (for fumagillin production).

Question. How does the application of cyanobacteria help to improve agriculture output?
Answer: Cyanobacteria are autotrophic, free-living or symbiotic microbes. They can fix atmospheric nitrogen. Blue-green algae also add organic matter to the soil and increases its fertility. They replenish soil nutrients and reduce dependence on chemical fertilisers.

Question. How do mycorrhizae act as biofertilisers? Explain. Name a genus of fungi that forms a mycorrhizal association with plants. 
Answer: Mycorrhizae is a symbiotic association of a fungus with roots of higher plants. The fungus absorbs phosphate from soil and passes it to the plant. It also provides resistance to root-borne pathogen and increase the tolerance of plant to salinity and drought. This way they act as biofertilisers.
Genus of fungi — Glomus.

Question. Find out the role of microbes in the following and discuss it with your teacher.
(a) Single cell protein (SCP)
(b) Soil
Answer: (a) Single cell protein (SCP): It is a protein-rich microbial biomass which can be used as food.
SCP contains essential amino acids and low fat. Bacteria, filamentous fungi, algae, yeast,etc., are used as “single cell proteins” (SCPs). Spirulina is taken as a tablet having 60 per cent proteins, all minerals, vitamins, etc.
(b) Soil: Soil is the habitat of numerous microbes. Microbes in the soil increase the fertility of soil by decomposing organic matter. Some microbes convert nitrates into free nitrogen that escapes into atmosphere for replenishment.

Question. Your advice is sought to improve the nitrogen content of the soil to be used for cultivation of a non-leguminous terrestrial crop.
(a) Recommend two microbes that can enrich the soil with nitrogen.
(b) Why do leguminous crops not require such enrichment of the soil? 
Answer: (a) Azospirillum/Azotobacter/Anabaena/Nostoc/Oscillatoria/Frankia. (Any two)
(b) Leguminous crops do not need nitrogen from soil because the nitrogen fixing bacteria (Rhizobium) are present in their root nodules, which can fix atmospheric nitrogen for the crops.

Question. How does the application of the fungal genus, Glomus, to the agricultural farm increase the farm output? 
Answer: Glomus is a fungus which is found in symbiotic relationship with roots of seed plants. It absorbs phosphorus from the soil and passes it on to the plant, and in turn gets sugars from the plant. Due to increased availability of phosphorus there is an increase in farm output.

Question. How was penicillin discovered? 
Answer: Penicillin was an accidental discovery. Sir Alexander Fleming observed that in unwanted culture plates of Staphylococcus a mould of Penicillium was growing This mould inhibited the growth of Staphylococcus around it. Later the antibiotic penicillin was isolated from this fungus.

Question. Complete the given table.

Answer: (i) Citric acid
(ii) Saccharomyces cerevisiae
(iii) Trichoderma polysporum
(iv) Acetobacter aceti
(v) Statin
(vi) Streptokinase

Question. Why should biological control of pests and pathogens be preferred to the conventional use of chemical pesticides? Explain how the following microbes act as biocontrol agents:
(a) Bacillus thuringiensis
(b) Nucleopolyhedrovirus
Answer: Biological control of pests and pathogens is preferred because:
(i) The chemicals cause pollution of water bodies as well as ground water, besides getting stored in the plants.
(ii) The chemicals are toxic thus extremely harmful to human beings and other animals.
(a) Bacillus thuringiensis: Bacillus thuringiensis is available in sachets as dried spores, which are mixed with water and sprayed onto vulnerable plants. When they are eaten by the insect larvae, the toxin is released in the gut where it becomes active and kills the larvae.
B. thuringiensis toxin genes when introduced into plant, develop resistance to attack by insect pests. Specific Bt toxin genes obtained from B. thuringiensis are used in several crop plants which make them resistant to insect pest.
(b) Nucleopolyhedrovirus: These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management (IPM) programme.

Question. Name the genus to which baculoviruses belong. Describe their role in the integrated pest management programmes. 
Answer: Baculovirus belongs to the genus Nucleopolyhedrovirus. Baculoviruses are pathogens that attack insects and other arthopods. These viruses are very useful for species-specific, narrow spectrum insecticidal applications. Also, as they show no negative impacts on plants, mammals, birds, fish or even on non-target insects, they are beneficial in integrated pest management (IPM) programme in which beneficial insects are conserved.

Question. Explain the different steps involved in sewage treatment before it can be released into natural water bodies. 
                                                    ​​​​​​​OR
Describe the process of waste-water treatment under the following heads:
(a) Primary treatment
(b) Secondary treatment 
                  OR
Explain the process of sewage water treatment before it can be discharged into natural water bodies. Why is this treatment essential? 
Answer: Primary treatment or physical treatment
• It is the physical removal of large and small particles from sewage.
• First, the floating debris is removed by sequential filtration by passing through wire mesh screens.
• Then, the grit (soil and small pebbles) are removed by sedimentation in settling tanks. The sediment is called primary sludge and the supernatant is the effluent.
• The effluent is taken for secondary treatment.
The sewage treatment is essential before being released into water bodies so as to check water borne diseases or pathogenic organisms due to water pollution.

Question. Explain the significant role of the genus Nucleopolyhedrovirus in an ecological sensitive area.
Answer: Baculoviruses are pathogens that attack insects and other arthropods. Baculoviruses of genus Nucleopolyhedrovirus are used as biological control agents. They are excellent candidates for species-specific, narrow spectrum insecticidal applications. They do not show negative impact on plants, mammals, birds, non-target insects. Therefore, they are used as biological control agents.
Importance in organic farming: It is desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) programme. In organic farming, it is used to conserve beneficial insects and kills harmful ones.

Question. List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment. 
                                                    ​​​​​​​                          OR
Explain the process of secondary treatment given to the primary effluent up to the point it shows significant change in the level of biological oxygen demand (BOD) in it. 
Answer: During secondary treatment of primary effluents, vigorous growth of useful aerobic microbes into flocs occur when it is agitated mechanically and air is pumped into it in a large aeration tank. These microbes while growing consume major part of the organic matter in the effluent. This significantly reduces BOD.

Question. Describe how do ‘flocs’ and ‘activated sludge’ help in sewage treatment. 
Answer: Flocs are masses of aerobic bacteria associated with fungal filaments to form mesh like structures.
These aerobic microbes consume the major part of the organic matter in the effluent. This significantly reduces Biological oxygen demand (BOD) of the effluent.
A small part of the activated sludge is used as inoculum and pumped back to aeration tank. The remaining major part of the sludge is pumped into anaerobic sludge digesters where microbes or bacteria grow anaerobically to produce CH₄ or H₂S or CO₂ or biogas.